1. Claim For Priority
This application claims priority to Korean Patent Application No. 10-2006-0014322 filed on Feb. 14, 2006, in the Korean Intellectual Property Office (KIPO), the entire contents of which are hereby incorporated by reference.
2. Field of the Invention
The present invention relates to an apparatus and method for forming a predetermined pattern on a substrate using a gravure offset printing method.
3. Description of the Related Art
As various kinds of portable electronic equipment such as a mobile phone, person digital assistant (PDA) and notebook computer have been recently developed, a demand for a flat panel display having lightweight, thin and short and compact features is gradually increased. A flat panel display such as LCD (liquid crystal display), PDP (plasma display panel), FED (field emission display) and VFD (vacuum fluorescent display) have been actively studied and currently put to practical use.
In general, the flat panel display is formed with a color filter layer for implementing a color image thereon, and comprises a color filter in which a black matrix is formed to prevent an image quality thereof from being deteriorated due to leakage of light to a region excluding an image display area. A typical flat panel display including such a color filter is a liquid crystal display device. Such a liquid crystal display device is composed of a thin film transistor substrate with a thin film transistor formed thereon and a color filter substrate with a color filter layer formed thereon, and is completed by injecting liquid crystal between the two substrates to form a liquid crystal layer.
In the meantime, pixels having R (red), G (green) and B (blue) color components are generally arranged in a color filter layer 1, as shown in FIGS. 1 and 2. At this time, each of the pixels in the liquid crystal display device may be composed of sub-pixels with R, G and B color components. However, each pixel generally has a single color. The arrangement of pixels can be variously made according to the difference of resolution. Such a color filter layer can be formed through various methods such as dyeing, printing, electrodepositing and pigment spraying methods. In a conventional STN (super-twisted nematic) liquid crystal display device, the color filter layer has been mainly formed through the dyeing, printing or electrodepositing method. On the other hand, in a TFT LCD with excellent delicacy and reproducibility and applicability to a large-sized liquid crystal panel, the pigment spraying method is mainly utilized.
In the pigment spraying method, a photosensitive color resist is formed into a pattern through a typical photolithographic process to form the color filter layer. That is, the photosensitive color resist is first applied on a substrate, light is then irradiated onto the color resist using a mask, and a desired pattern is finally formed using developer, whereby the color filter layer has been completed. Therefore, the photolithographic process is required in forming the color filter through the pigment spraying method. However, there are some problems in that the photolithographic process is complicated and excessive manufacturing costs are required. Furthermore, the photolithographic process should be repeated three times to form the R, G and B pixels, and thus, a manufacturing process becomes more complicated.
In order to overcome the aforementioned problems in such a pigment spraying method, a scheme in which a printing method is employed in the TFT LCD field has been recently proposed. That is, a plurality of gravures, each filled with a color resist, and a plurality of rollers corresponding to the gravures are provided such that a color resist pattern with a certain color component is formed on a substrate by means of a roller, and the other color resists are sequentially formed by means of the other relevant rollers.
The above process will be described in more detail with reference to FIG. 3, as follow.
First, as shown in FIG. 3(a), an adequate amount of color resist R is supplied onto a surface of a gravure 10 on which a pattern of a predetermined color component is formed. At this time, an amount of the color resist R supplied onto the gravure is slightly greater than a volume of a pattern groove 12 formed on the surface of the gravure 10. Then, a doctor blade 20 is employed such that the color resist R is received only in the pattern groove 12 formed on the surface of the gravure 10, and the color resist remaining on the other region is removed.
After the color resist R has been filled as such, a roller 30 is rolled along the surface of the gravure 10 as shown in FIG. 3(b) such that the pattern of the color resist R formed on the surface of the gravure is transferred onto the roller.
Then, the roller 30 onto which the color resist pattern has been transferred is moved on a substrate 40, and the pattern of the color resist R transferred to the surface of the roller 30 is transferred again onto the substrate 40 as shown in FIG. 3(c). Consequently, a predetermined color resist pattern is formed on the substrate 40 in such a manner. The aforementioned process is repeated three times to form the R, G and B patterns on the substrate.
In order to manufacture the color filter in such a manner, the roller is rotated at a predetermined speed and moved in a horizontal direction. At this time, a rotating speed and a horizontally moving speed of the roller should be controlled precisely such that the color resist pattern formed on the roller can be transferred onto the substrate without any change.
As shown in FIG. 4, a roller 10 has been conventionally designed in such a manner that it is rotated and linearly moved using a pinion gear 14 and a rack 16. However, in a case where the pinion gear 14 and the rack 16 are utilized, there is a problem in that large noise is generated while the roller is driven. Further, there is another problem in that it is difficult to accurately control the roller due to tolerance and backlash by means of an error made in the process of machining the gear.